Malaria is an old infectious disease caused by four protozoan parasites, Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae and Plasmodium ovale. These four parasites are typically transmitted by the bite of an infected female Anopheles mosquito. Malaria is a problem in many parts of the world, and over the last few decades the malaria burden has steadily increased. An estimated 1 to 3 million people die every year from malaria—mostly children under the age of 5. This increase in malaria mortality is due in part to the fact that Plasmodium falciparum, the deadliest malaria parasite, has acquired resistance against nearly all available antimalarial drugs, with the exception of the artemisinin derivatives.
Leishmaniasis is caused by one of more than twenty (20) varieties of parasitic protozoa that belong to the genus Leishmania, and is transmitted by the bite of female sandflies. Leishmaniasis is endemic in some 90 countries, including many tropical and sub-tropical areas.
There are four main forms of leishmaniasis. Visceral leishmaniasis, also called kala-azar, is the most serious form and is caused by the parasite Leishmania donovani. Patients who develop visceral leishmaniasis can die within months unless they receive treatment. The two main therapies for visceral leishmaniasis are the antimony derivatives sodium stibogluconate (Pentostam®) and meglumine antimoniate (Glucantim®). Sodium stibogluconate has been used for about 70 years and resistance to this drug is a growing problem. In addition, the treatment is relatively long and painful, and can cause undesirable side effects.
Human African Trypanosomiasis, also known as sleeping sickness, is a vector-borne parasitic disease. The parasites concerned are protozoa belonging to the Trypanosoma Genus. They are transmitted to humans by tsetse fly (Glossina Genus) bites which have acquired their infection from human beings or from animals harbouring the human pathogenic parasites.
Chagas disease (also called American trypanosomiasis) is another human parasitic disease that is endemic amongst poor populations on the American continent. The disease is caused by the protozoan parasite Trypanosoma cruzi, which is transmitted to humans by blood-sucking insects. The human disease occurs in two stages: the acute stage, which occurs shortly after the infection, and the chronic stage, which can develop over many years. Chronic infections result in various neurological disorders, including dementia, damage to the heart muscle and sometimes dilation of the digestive tract, as well as weight loss. Untreated, the chronic disease is often fatal.
The drugs currently available for treating Chagas disease are nifurtimox and benznidazole. However, problems with these current therapies include their adverse side effects, the length of treatment, and the requirement for medical supervision during treatment. Furthermore, treatment is really only effective when given during the acute stage of the disease. Resistance to the two frontline drugs has already arisen. The antifungal agent amphotericin b has been proposed as a second-line drug, but this drug is costly and relatively toxic.
In view of the foregoing, it is desirable to develop novel compounds for evaluation and use as antiparasitic agents.